1. Field of the Invention
The present disclosure generally relates to micro-fluid ejection devices, such as inkjet printers. More particularly, although not exclusively, it relates to spray coatable adhesive used for bonding silicon chips of ejection heads to rigid substrates.
2. Description of the Related Art
In the field of micro-fluid ejection devices, ink jet printers are an example application where miniaturization continues to be pursued. This includes miniaturization of ejection chips or dies to reduce material cost of ejection heads. In reducing the ejection chip size, it is usually the chip width that must be decreased while the chip length would be tailored to the cost/performance requirements of a particular printing application. These ejection chips are typically coupled with a rigid support substrate such as a silicon substrate having one or more flow features. So as ejection chips get smaller, the bonding and sealing widths to the support this rigid silicon substrate must be reduced to less than 500 microns. This miniaturization of ejection chips then leads to challenges relating to techniques and adhesive used for bonding the chips on the support substrate. This bonding must provide narrow and robust seals and proper chip alignment to flow features of the support substrate.
A typical way of bonding chips to a substrate is to dispense a die attach adhesive onto the substrate through a needle. This type of die attach adhesive has a high viscosity ranging from about 60,000 to 100,000 centipose (cps) in which the smallest bond width it can reliably provide upon dispensed and prior to mounting of the chip, are in the range of 450-500 μm. It becomes difficult to dispense such adhesives onto a densely patterned substrate allowing a bond line and sealing width much smaller than the adhesive dispensing width. It would be advantageous to provide an adhesive composition having low viscosity which is spray to coatable and can be uniformly applied on a substrate having through holes and channels, form a robust seal with narrow widths, allow precise alignment of chips on a substrate, and has good compatibility with an ink jet printer environment. Thus, there continuous to be a need for improved adhesive composition and bonding techniques for miniaturized ejection head components of ink jet printers. This is especially true when a rigid silicon chip needs to be bonded onto a silicon substrate.